Machine tool

ABSTRACT

To provide a machine tool in which supporting stiffness of a tool post is increased, thereby enabling improvement in machining accuracy. When seen in a Z-axis direction, a tool post  5  includes: a supporting member  30  having a pair of left and right leg parts  30   a,    30   a  and an upper beam part  30   b  coupling at least upper ends of the both leg parts  30   a  with each other; and a turret  31  to whose outer circumferential portion a plurality of tools are attached. The supporting member  30  is supported to be movable in a Z-axis direction between a first and a second spindle headstock  3, 4 , and the turret  31  is supported to be movable in an X-axis direction by turret guide rails  33, 33  which are disposed on front faces of the left and right leg parts  30   a,    30   a.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a machine tool including: a firstspindle headstock disposed on a bed; a moving table disposed coaxiallywith the first spindle headstock; and a tool post disposed between thefirst spindle headstock and the moving table.

2. Description of the Related Art

An example of a machine tool of this type is structured such that aspindle headstock is fixedly disposed on a left end portion of a bedwhen seen from a front side of the machine and a lower tool post and anupper tool post are disposed on a lower side and an upper side of a toolpost supporting part in a slanted shape respectively. The lower toolpost is structured such that a lower saddle is supported to be movablein a spindle axis (Z-axis) direction by a Z-axis guide which is disposedon the tool post supporting part and a tool post main body is supportedto be movable in a direction (X-axis direction) parallel to a supportingsurface of the slanted shape and perpendicular to the spindle axis, byan X-axis guide which is disposed on the lower saddle (see, for example,Patent document 1).

[Patent document 1] Japanese Patent Application Laid-open No. Hei6-106438

Incidentally, the aforesaid conventional lathe adopts a structure suchthat the lower tool post, which is a heavy object, is supported by theslanted tool post supporting part to be movable in the Z-axis directionand the X-axis direction, and a cutting direction by the lower tool postis parallel to the slanted surface. Therefore, a reaction force of thecutting force of the lower tool post acts in parallel to the slantedsurface. As a result, the aforesaid conventional machine has a problemof difficulty in ensuring supporting stiffness in the cutting directionof the lower tool post, which in some cases may possibly result inlowered machining accuracy.

SUMMARY OF THE INVENTION

The present invention was made in consideration of the abovecircumstances and it is an object thereof to provide a machine toolcapable of realizing increased supporting stiff in a cutting directionof a tool post and as a result, capable of realizing enhanced machiningaccuracy.

In an invention, a machine tool includes: a bed; a first spindleheadstock disposed on the bed; a moving table disposed to be coaxialwith the first spindle headstock and to be movable in an axis (Z-axis)direction; and a tool post disposed between the first spindle headstockand the moving table, wherein the tool post includes: a supportingmember having a pair of left and right leg parts when seen in the axisdirection and a beam part integrally coupling at least upper ends of theboth leg parts with each other; and a turret to whose outercircumferential portion a plurality of tools are attached and which issupported by the supporting member, and wherein the supporting member issupported on the bed to be movable in the axis direction, and the turretis supported to be movable in an up/down (X-axis) direction by turretguide rails disposed on front faces or side faces of the left and rightleg parts.

In the invention, the supporting member has the pair of left and rightleg parts and the beam part coupling at least the upper ends of the bothleg parts, and the turret is supported to be movable in the up/downdirection by the turret guide rails disposed on the front faces or sidefaces of the left and right leg parts, so that a reaction force of acutting force by the tool post acts perpendicularly to a surface of thebed supporting the supporting member. As a result, the present inventioncan increase supporting stiffness in the cutting direction of the toolpost to enhance machining accuracy.

Further, the turret is supported by the turret guide rails disposed onthe front faces or side faces of the left and right leg parts, so that asupporting position of the turret and a cutting point can be made closeto each other, which can also enhance machining accuracy.

In a preferable embodiment of the invention, a cutting point of the toolpost is positioned vertically under the first spindle headstock.

In the above-described embodiment, the cutting point of the tool post ispositioned vertically under the axis of the first spindle headstock, sothat the reaction force in the cutting force of the tool post can bemore surely made perpendicular to the surface of the bed. Therefore, itis possible to more surely increase supporting stiffness of the toolpost to more enhance machining accuracy.

In another preferable embodiment of the invention, the supporting memberis mounted on a guide rail by which the moving table is supported to bemovable in the axis direction, lower portions of the left and right legparts widen outward in a radial direction of the turret and protrudetoward the moving table side across the turret guide rails, and theturret guide rails are disposed on the front faces of the left and rightleg parts.

In the above-described embodiment, the supporting member is movablymounted on the guide rail movably supporting the moving table, so thatthe guide rail for the moving table can also serve as the guide rail forthe supporting member. Therefore, the number of parts and cost can bereduced.

Further, the lower portions of the left and right leg parts widenoutward in the radial direction of the turret and protrude toward themoving table side across the turret guide rails, so that supportingstiffness of the turret can be more increased.

Specifically, a large overturning moment acts on the supporting memberby the weight of the turret and the reaction force of the cutting force,but portions protruding toward the moving table, which are formed in thelower portions of the leg parts, can efficiently receive the overturningmoment. As a result, supporting stiffness of the turret is increased.

Further, the turret guide rails are disposed on the front faces of theleft and right leg parts, so that the supporting position of the turretcan be made closer to the cutting point, which can also enhancemachining accuracy more.

In still another preferable embodiment of the invention, a turret ballscrew moving the turret in the up/down direction and a feed motor rotarydriving the turret ball screw are disposed to be deviated toward oneside in a left/right direction in a space surrounded by the left andright leg parts and the beam part of the supporting member.

In the above-described embodiment, the turret ball screw and the feedmotor are disposed in the space surrounded by the left and right legparts and the beam part of the supporting member, being deviated towardone side in the left/right direction, so that a vacant space in thesupporting member made available owing to this structure can be utilizedas arrangement space for piping, wiring, and so on.

In still another preferable embodiment of the invention, the turretincludes: a turret head to which the tools are attached; and a rotaryindexing mechanism by which the turret head is supported to be rotaryindexable, and wherein a rotary indexing motor of the rotary indexingmechanism is disposed on a back face of the turret and is positioned inthe space surrounded by the left and right leg parts and the beam partof the supporting member.

In the above-described embodiment, the rotary indexing motor of therotary indexing mechanism for the turret head is disposed so as to bepositioned in the space formed on the back face of the turret, so thatthe space formed in the supporting member can be effectively used fordisposing the rotary indexing motor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a composite lathe according to oneembodiment of the present invention;

FIG. 2 is a side view of the composite lathe;

FIG. 3 is a perspective view of a bed of the composite lathe;

FIG. 4 is a perspective view of the bed;

FIG. 5 is a front view of a supporting mechanism for a third spindle ofthe composite lathe;

FIG. 6 is a side view of a first spindle headstock and a tool postdisposed on the bed;

FIG. 7(a), FIG. 7(b), and FIG. 7(c) are views showing operations of thefirst spindle headstock, a second spindle headstock, and the tool post;

FIG. 8 is a perspective view of the first spindle headstock;

FIG. 9 is a perspective view of the first spindle headstock;

FIG. 10 is a perspective view of the first spindle headstock;

FIG. 11(a) and FIG. 11(b) are views of the first spindle headstock;

FIG. 12 is a perspective view of a cooling oil jacket of the firstspindle headstock;

FIG. 13 is a perspective view of the tool post;

FIG. 14 is a side view of the tool post;

FIG. 15 is a front view of the tool post;

FIG. 16 is a perspective view of a supporting member of the tool post;

FIG. 17 is a perspective view showing an X-axis stroke of the thirdspindle; and

FIG. 18 is a side view showing a Y-axis stroke of the third spindle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the present invention will be hereinafter describedbased on the attached drawings.

FIG. 1 to FIG. 18 are views to illustrate a composite lathe according toone embodiment of the present invention. FIG. 1 and FIG. 2 are aperspective view and a right side view of the composite latherespectively, FIG. 3 and FIG. 4 are perspective views of a bed on whicha first spindle headstock and a tool post are mounted, FIG. 5 is a frontview of a supporting mechanism supporting a third spindle, FIG. 6 is aright side view of the first spindle headstock and the tool post, FIG.7(a) to FIG. 7(c) are front views showing operations of the firstspindle headstock, a second spindle headstock, and the tool post, FIG. 8to FIGS. 11(a), (b) are views of the first spindle headstock, FIG. 12 isa perspective view of a cooling oil jacket of the first spindleheadstock, FIG. 13 to FIG. 16 are views of the tool post, and FIG. 17and FIG. 18 are views showing X-axis and Y-axis direction strokes of thethird spindle. Note that front/back and left/right mentioned in thisembodiment mean front/back and left/right when the machine is seen froma front side, unless otherwise noted.

In the drawings, 1 denotes the composite lathe. When seen from the frontside of the machine shown in FIG. 1, the composite lathe 1 includes: abed 2; a first spindle headstock 3 disposed on a left end portion on thebed 2; a second spindle headstock 4 disposed on the right side of thefirst spindle headstock 3 to be coaxial with the first spindle headstock3 and to be movable in a Z-axis (left/right) direction; a tool post 5disposed between the first and second spindle headstocks 3, 4 to bemovable in an X-axis (up/down) direction and in the Z-axis direction;and a third spindle 6 disposed on the bed 2 to be movable in the X-axisdirection, a Y-axis (front/back) direction, and the Z-axis direction. Ona back left end portion on the bed 2, provided is a tool changer 7automatically changing a preceding-process tool attached to the thirdspindle 6 to a subsequent-process tool.

As shown in FIG. 3, the bed 2 is constituted of a front bed part 2 a anda back bed part 2 b which are integrally molded. A first and a secondmounting surface 2 a′, 2 a″ are formed on the front bed part 2 a andthird mounting surfaces 2 b′ are formed on the back bed part 2 b, allthese surfaces being horizontal along the Z-axis direction and theY-axis direction.

Compared with the second mounting surface 2 a″ of the front bed part 2a, the first mounting surface 2 a′ is positioned higher than the secondmounting surface 2 a″, and the third mounting surfaces 2 b′ of the backbed part 2 b are positioned lower than the first mounting surface 2 a′and higher than the second mounting surface 2 a″, so that they areformed in a stepped manner.

The first spindle headstock 3 is mounted on the first mounting surface 2a′. On the second mounting surface 2 a″, the second spindle headstock 4and the tool post 5 are mounted to be movable in the Z-axis direction.Further, on the third mounting surfaces 2 b′, a supporting mechanism 10movably supporting the third spindle 6 is mounted.

The supporting mechanism 10 includes: a column 11 in a rectangular frameshape which is fixed on the third mounting surfaces 2 b′ of the back bedpart 2 b to extend vertically upward; a saddle 12 in a rectangular frameshape which is supported on a front face of the column 11 to be movablein the Z-axis direction; a cross slide 13 supported on a front face ofthe saddle 12 to be movable in the X-axis direction; and a ram 14supported by the cross slide 13 to be movable in the Y-axis directionand supporting the third spindle 6.

The column 11 is structured such that left and right support posts 11 c,11 d and upper and lower beam parts 11 a, 11 b, which couple upper andlower ends of the left and right support posts 11 c, 11 d, areintegrally molded. The column 11 is firmly fixed on the third mountingsurfaces 2 b′ of the back bed part 2 b.

Similarly to the column 11, the saddle 12 is structured such that leftand right support posts 12 a, 12 b and upper and lower beam parts 12 c,12 d, which couple upper and lower ends of the left and right supportposts 12 a, 12 b, are integrally molded. The saddle 12 is supported tobe movable in the Z-axis direction by a pair of upper and lower Z-axisguide rails 15, 15 which are disposed in parallel to the Z-axis on frontfaces of the upper and lower beam parts 11 a, 11 b of the column 11.Z-axis ball screws 16, 16 are screwed to nut parts 12 e, 12 e formed inthe upper and lower beam parts 12 c, 12 d of the saddle 12. The saddle12 is driven to reciprocate in the Z-axis direction when the Z-axis ballscrews 16, 16 are rotary driven by servo motors 16 a, 16 a. Note thatthe Z-axis ball screws 16, 16 are disposed in parallel to the Z-axis onthe front faces of the upper and lower beam parts 11 a, 11 b of thecolumn 11.

The cross slide 13 is formed in a rectangular thick plate shape and issupported to be movable in the X-axis direction by a pair of left andright X-axis guide rails 17, 17 which are disposed in parallel to the Xaxis on the front faces of the left and right support posts 12 a, 12 bof the saddle 12. X-axis ball screws 18, 18 are screwed to nut partsformed on left and right sides of the cross slide 13. The cross slide 13is driven to reciprocate in the X-axis direction when the X-axis ballscrews 18, 18 are rotary driven by servo motors 18 a, 18 a. Note thatthe X-axis ball screws 18, 18 are disposed in parallel to the X-axis onthe front faces of the left and right support posts 12 a, 12 a of thesaddle 12.

The ram 14 is inserted in a ram guide hole 13 a formed in the crossslide 13 and is supported to be movable in the Y-axis direction by guideplates (not shown) which are arranged on an inner circumferentialsurface of the ram guide hole 13 a, being a predetermined angle apartfrom one another. One Y-axis ball screw 21 disposed in a lower portionof a widthwise center of the cross slide 13 is screwed to a nut part ofthe ram 14. The ram 14 is driven to reciprocate in the Y-axis directionwhen the Y-axis ball screw 21 is rotary driven by a servo motor.

The third spindle 6 is rotatably inserted in the ram 14. At a tip of thethird spindle 6, a tool spindle 6 a is disposed, with its axis directedperpendicularly to the Y axis. A tool is attached to a tip of the toolspindle 6 a and the tool spindle 6 a is rotary driven by a driving motor6 b. Further, the third spindle 6 can be rotary indexed around the Yaxis (B axis) for positioning by a built-in rotary indexing mechanism(not shown).

The front bed part 2 a includes: a first mounting part 2 d having thefirst mounting surface 2 a′ formed on an upper surface thereof; and asecond mounting part 2 e having the second mounting surface 2 a″ whichis formed so as to be positioned lower than the first mounting surface 2a′.

The first mounting part 2 d has a recession 2 f continuing from thesecond mounting surface 2 a″, and a bottom of the recession 2 f is flushwith the second mounting surface 2 a″. Therefore, the first mountingsurface 2 a′ is in a U-shape when seen from above.

Further, a center trough 2 c in a groove form whose upper side is openis formed in a front/back-direction center portion of the secondmounting surface 2 a″ of the front bed part 2 a. At a right wall of thefront bed part 2 a, the center trough 2 c is open to the outside. In thecenter trough 2 c, a chip conveyer (not shown) conveying chips to theoutside through the opening is disposed.

On the second mounting surface 2 a″ of the front bed part 2 a, a pair offront and back second spindle guide rails 24, 24, by which the secondspindle headstock 4 is supported to be movable in the Z-axis direction,are disposed in parallel to the Z axis. The second spindle guide rails24 both extend to the inside of the recession 2 f of the first mountingpart 2 d. On an inner side of and adjacently to the front-side guiderail 24 out of the both second spindle guide rails 24, one secondspindle ball screw 25 is disposed to drive the Z-axis directionreciprocal movement of the second spindle headstock 4. Further, on aninner side and adjacently to the opposite guide rail 24, one tool postball screw 32 is disposed to drive the Z-axis direction reciprocalmovement of the tool post 5.

The second spindle headstock 4 includes: a movable base 4 a mounted onthe second spindle guide rails 24, 24 to be slidable in the Z-axisdirection; and a spindle headstock main body 4 b fixed on the movablebase 4 a and having a cylindrical part. A second spindle 26 facing thefirst spindle headstock 3 is rotatably inserted in the spindle headstockmain body 4 b. The second spindle 26 includes a chuck 26 a holding aworkpiece and is rotary driven by a built-in driving motor.

When seen in the Z-axis direction, the first spindle headstock 3includes: left and right leg parts 3 a, 3 a in a wide flat plate shapepositioned on the left and right; a cylindrical spindle case part 3 bcoupling upper ends of the leg parts 3 a; and a coupling part 3 ccoupling the spindle case part 3 b and the left and right leg parts 3 a,3 a on an opposite side of the second spindle headstock 4, and thesecomponents of the first spindle headstock 3 are integrally molded.Therefore, a tunnel part 3 d surrounded by the leg parts 3 a, thespindle case part 3 b, and the coupling part 3 c is formed in the firstspindle headstock 3.

When seen from above, the coupling part 3 c forms a V-shape continuingfrom the left and right leg parts 3 a to extend to the opposite side ofthe second spindle headstock 4, and when seen from the side, it forms atriangular shape continuing from the spindle case part 3 b to widentoward an obliquely downward direction. A flange part 3 e protrudingoutward is integrally formed along the whole periphery of lower ends ofthe left and right leg parts 3 a, 3 a and the coupling part 3 c. Theflange part 3 e is fixedly bolted to the first mounting surface 2 a′.

The first spindle headstock 3 is formed to be thermally symmetrical.Here, “thermally symmetrical” means a state in which a left portion anda right portion across a plane of symmetry are substantially equal inthermal expansion amount and the whole structure expands along thisplane of symmetry. Concretely, when a cross section taken along a planeincluding the X axis and the Y axis is seen in the Z-axis direction (seeFIG. 11(a)), a plane including a vertical line “b” going through an axis“a” of the spindle case part 3 b is a plane of symmetry, and the leftand right leg parts 3 a, 3 a, the coupling part 3 c, and the spindlecase part 3 b are formed to be almost laterally symmetrical with respectto the plane of symmetry. With this structure, the first spindleheadstock 3 thermally expands only in the direction of the vertical line“b”.

On the other hand, when a cross section of the first spindle headstock 3taken along a plane including the X axis and the Z axis is seen in theY-axis direction, the cross section is not symmetrical (see FIG. 11 (b))in this embodiment. Therefore, strictly speaking, the aforesaid thermalsymmetry is difficult to realize. Therefore, this embodiment adopts astructure such that a cooling oil jacket 40 is formed in the firstspindle headstock 3 as shown in FIG. 12 to more surely realize theaforesaid thermal symmetry by cooling by the cooling oil jacket 40.

Specifically, in the cooling structure of this embodiment, the leg parts3 a, 3 a and the coupling part 3 c are more surely cooled by a largeamount of cooling oil than the spindle case part 3 b so that theaforesaid axis “a” moves upward along the vertical line “b” due tothermal expansion. Concretely, the cooling oil jacket 40 has: a spindlecooling oil passage 40 a in a coiled shape formed on an outercircumferential portion of the spindle case part 3 b; a pair of upperand lower upper leg cooling oil passages 40 b, 40 b formed along anupper portion of each of the left and right leg parts 3 a, 3 a; lowerleg cooling oil passages 40 c, 40 c formed along lower portions of theleft and right leg parts 3 a, 3 a; and a coupling part cooling oilpassage 40 d formed along a lower portion of the coupling part 3 c.Compared with the spindle cooling oil passage 40 a, the other coolingoil passages 40 b to 40 d are larger in diameter. This structure makesit possible to more surely cool the leg parts 3 a, 3 a which maypossibly hinder the realization of the aforesaid thermal symmetry, sothat as a whole, the first spindle headstock 3 can expand only in theupward direction along the vertical line “b”.

The cooling oil is supplied from a supply port provided in the middle ofthe upper cooling oil passage 40 b disposed on a back side in FIG. 12.The cooling oil moves in the right direction in the drawing in the uppercooling oil passage 40 b, moves in the left direction in the drawing inthe cooling oil passage 40 b immediately under via an external pipe,goes down, moves in 40 c on the back side in the drawing and 40 d, movesin 40 c on the front side in the drawing, goes up, moves in the rightdirection in the lower-side 40 b disposed on the front side in thedrawing, moves in the left direction in 40 b immediately above via anexternal pipe, moves spirally in 40 a, and is discharged from an outletformed in 40 a.

A first spindle 28 is rotatably inserted in the spindle case part 3 b tobe coaxial with the second spindle 26. The first spindle 28 includes achuck 28 a holding a workpiece and is rotary driven by a built-indriving motor.

A presetter 38 is further attached to the first spindle headstock 3, asshown in FIG. 8 The presetter 38 is intended for measuring a blade edgeposition of a tool before machining and it performs the measurement bothfor a tool of a turret 31 and for a tool of the third spindle 6, as willbe described later.

The tool post 5 has the turret 31 and a supporting member 30 by whichthe turret 31 is supported to be movable in the X-axis direction. Theturret 31 includes: a turret head 31 a to whose outer circumferentialportion a large number of tools T are attached, being a predeterminedangle apart from one another; and a rotary indexing mechanism 31 bsupporting the turret head 31 a rotary indexably. The rotary indexingmechanism 31 b rotary-indexes a desired tool T at a predeterminedmachining position to clamp it at the machining position. An indexingmotor 31 c of the rotary indexing mechanism 31 b is disposed on a backface of the turret 31 when seen from the right side in the Z-axisdirection.

The supporting member 30 is a molded product in a rectangular frameshape and has: left and right leg parts 30 a, 30 a positioned on theleft and right when seen in the Z-axis direction; an upper beam part 30b integrally coupling upper ends of the both leg parts 30 a, 30 a; and alower beam part 30 c integrally coupling lower ends thereof. Therefore,a portion inside the frame of the supporting member 30 is a rectangularspace.

The respective leg parts 30 a have: vertical wall parts 30 d, 30 d in awide flat plate shape; and supporting parts 30 e, 30 e formed in lowerportions of outer walls of the respective vertical wall parts 30 d andextending in the Z-axis direction. When seen in the Y-axis direction,left ends 30 f of the respective supporting parts 30 e are in line withleft end faces of the vertical wall parts 30 d, while right ends 30 f′thereof extend up to the vicinity of a center portion of the turret head31 a across right end faces of the vertical wall parts 30 d.

In the supporting member 30, linear guides 30 g disposed on bottom facesof longitudinal both ends of the respective supporting parts 30 e, 30 eare supported by the aforesaid front and back second spindle guide rails24, 24, so that the supporting member 30 is movable in the Z-axisdirection. Further, a nut member 30 h is disposed in a lower portion ofthe right supporting part 30 e, and the tool post ball screw 32 providedon the inner side of the back-side second spindle guide rail 24 isscrewed to the nut member 30 h. The supporting member 30 reciprocates inthe Z-axis direction when the tool post ball screw 32 is rotated by aservo motor 32 a.

When seen from a right side in the Z-axis direction, on front faces(faces on the front side) of the left and right leg parts 30 a, 30 a ofthe supporting member 30, provided are turret guide rails 33, 33extending in the X-axis direction. Linear guides 33 a, 33 a aresupported by the turret guide rails 33, 33 to be slidable in the X-axisdirection, and the linear guides 33 a are fixed on the back face of theturret 31. With this structure, the turret 31 is supported by thesupporting member 30 to be movable in the X-axis direction.

Further, one turret ball screw 34 is disposed in parallel to the X axisin the supporting member 30 so as to extend between the upper and lowerbeam parts 30 b, 30 c. A nut member 34 a is screwed to the turret ballscrew 34, and the nut member 34 a is integrally provided on the backface of the turret 31.

Further, in the supporting member 30, an extension part 30 f is formedin the lower beam part 30 c to extend in a backward direction from theleg part 30 a, and a servo motor 35 is disposed on the extension part 30f. The servo motor 35 is coupled to the turret ball screw 34 via atiming belt 36. The turret 31 reciprocates in the X-axis direction whenthe ball screw 34 is rotary driven by the servo motor 35.

Here, when seen in the Z-axis direction, as shown in FIG. 16, the turretball screw 34 and the servo motor 35 are disposed to be deviated towardthe right side from the center line of the supporting member 30.Therefore, a left portion of the rectangular space of the supportingmember 30 is a space where pipes, wiring, and so on can be arranged.Note that the indexing motor of the rotary indexing mechanism 31 b ispositioned in a substantially center portion in the rectangular space ofthe supporting member 30 and moves in accordance with the X-axisdirection movement of the turret 31.

The shape and dimension of the supporting member 30 are set so that itcan move into/out of the tunnel part 3 d of the first spindle headstock3. In a state in which the supporting member 30 is housed in the tunnelpart 3 d, the turret 31 is positioned right under the first spindle 28.To be in more detail, a cutting point by a tool positioned at themachining position out of the tools T attached to the turret 31 isconstantly positioned on the vertical line “b” going through theaforesaid axis “a”.

The second spindle headstock 4 is movable to a delivery position whereit can directly receive a workpiece attached to the first spindle 28 ofthe first spindle headstock 3. Concretely, the second spindle headstock4 is movable in the Z-axis direction up to a position so that frontfaces of the chucks of the first and second spindles 28, 26 abuttinglyface each other (see FIG. 7(c)).

When the first and second spindles 28, 26 abut on each other, the toolpost 5 can be positioned right under the first spindle headstock 3 sothat the cutting point “c” is positioned vertically under the axis “a”of the first and second spindle headstocks 3, 4. Therefore, a workpiececutting direction of the tool of the turret 31 is in line with thevertical line “b”. Concretely, when seen from the right side in theZ-axis direction, as shown in FIG. 6, the cutting point “c” and arotation center “d” of the turret 31 are collinear on the vertical line“b” going through the axis “a” of the first and second spindleheadstocks 3, 4. Further, the vertical line “b” goes through the centerof an interval between the second spindle guide rails 24, 24.

Further, a tool gripper of the third spindle 6 is constantly positionedwithin an area surrounded by the aforesaid pair of upper and lowerZ-axis guide rails 15, 15 and pair of left and right X-axis guide rails17, 17. A movement area of a cutting point of the third spindle 6overlaps a movement area of the cutting point “c” of the tool post 5 andfurther includes an area under the cutting point “c” when seen in theZ-axis direction.

Here, when seen from above, an XY supporting plane A (see FIG. 15)parallel to the X axis and the Y axis by which the turret 31 of the toolpost 5 is supported to be movable in the X-axis direction is orthogonalto an XZ supporting plane B (see FIG. 2) parallel to the X axis and theZ axis by which the third spindle 6 is supported to be movable in theX-axis direction. To be in more detail, the XY supporting plane A meansa plane including both sliding surfaces of the left and right turretguide rails 33, 33 of the supporting member 30. Further, the XZsupporting plane B means a plane including both sliding surfaces of theleft and right X-axis guide rails 17, 17 of the saddle 12.

Further, as shown in FIG. 2, an X-axis direction movement line (theaforesaid vertical line “b”) of the turret 31 in the tool post 5 isarranged a predetermined distance “t” apart in the Y-axis direction fromthe XZ supporting plane B of the third spindle 6. Further, as shown inFIG. 15, in a state where the third spindle 6 is machining the shortestworkpiece held on the first spindle headstock 3, an X-axis directionmovement line “f” of the third spindle 6 is arranged a predetermineddistance t′ apart from the XY supporting plane A of the turret 31.

In the composite lathe of this embodiment, while the workpiece isrotated by the first spindle headstock 3 or the second spindle headstock4, the tool post 5 cuts in the workpiece to perform cutting work and thethird spindle 6 performs machining such as grinding and boring.

According to the tool post 5 of this embodiment, the turret 31 issupported by the turret guide rails 33, 33 disposed on the front facesof the left and right leg parts 30 a, 30 a, and the cutting point “c” ofthe turret 31 is positioned vertically under the axis “a” of the firstspindle headstock 3 and the second spindle headstock 4 and is moved inthe X-axis direction. Therefore, in order to cut in the workpiece, theturret 31 is moved in the up/down (X-axis) direction, so that a reactionforce to the turret 31 works downward, namely, perpendicularly to thebed surface. Therefore, supporting stiffness of this tool post can bemade far greater than that of a conventional tool post mounted on aslanted supporting surface. As a result, machining accuracy can beenhanced.

In addition, in this embodiment, when seen from the right side in theZ-axis direction (see FIG. 16), the supporting member 30 has the pair ofleft and right leg parts 30 a, 30 a and the upper and lower beam parts30 b, 30 c integrally coupling the upper ends and lower ends of the bothleg parts 30 a, so that it is possible to increase stiffness of thesupporting member 30 itself to ensure supporting stiffness of the turret31 which is a heavy object. As a result, the high stiffness of the toolpost itself can also enhance machining accuracy.

Moreover, the turret guide rails 33, 33 are disposed on the front facesof the left and right leg parts 30 a, 30 a, so that a supporting pointof the turret 31 can be made close to the cutting point “c”, which canalso enhance machining accuracy.

In addition, the tool post 5 can be positioned right under the axis “a”of the first and second spindle headstocks 3, 4, so that the machinemain body can be made smaller in front/back-direction dimension comparedwith a conventional machine where a tool post is disposed on a frontside when seen from the front side of the machine. Therefore, downsizingcan be achieved.

In this embodiment, the supporting member 30 is mounted on the secondspindle guide rails 24, 24 movably supporting the second spindleheadstock 4, so that one pair of the guide rails can serve both forsupporting the second spindle headstock 4 and for supporting the toolpost 5. Therefore, the number of parts and cost can be reduced.

Further, the supporting parts 30 e formed in the lower portions of theleft and right leg parts 30 a, 30 a protrude up to the center portion ofthe turret head 31 a across the turret guide rails 33, so thatsupporting stiffness of the turret 31 which is a heavy object can bemore increased. Specifically, since the turret 31 overhangs from asupporting surface of the supporting member 30, a gravity center of theturret 31 is accordingly positioned apart in a front direction from thesupporting surface. Therefore, an overturning moment by the weight ofthe turret 31 and by the cutting reaction force acts on the supportingmember 30. In this embodiment, the right ends 30 f′ of the supportingparts 30 e are positioned near a position under the gravity center ofthe turret 31, so that the overturning moment can be efficientlyreceived, which accordingly can increase the supporting stiffness.

In this embodiment, the turret ball screw 34 and the servo motor 35driving the turret 31 are positioned to be deviated toward the rightside from the center line of the supporting member 30, so that the leftspace in the supporting member 30 made available by this arrangement canbe utilized as the arrangement space for the pipes, wiring, and so on.

In this embodiment, the rotary indexing motor 31 c driving the rotaryindexing of the turret head 31 a is disposed to be positioned inside theleft space of the supporting member 30, and thus the vacant space of thesupporting member 30 can be effectively used for arranging the motor 31c.

The above embodiment has described, as an example, the composite latheincluding not only the first and second spindles 28, 26 but also thethird spindle 6, but the present invention is also applicable to a latheincluding only the first and second spindles and to a lathe including atail stock instead of the second spindle headstock 4.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof.

The present embodiments are therefore to be considered in all respectsas illustrative and no restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

1. A machine tool comprising: a bed; a first spindle headstock disposedon said bed; a moving table disposed to be coaxial with said firstspindle headstock and to be movable in an axis (Z-axis) direction; and atool post disposed between said first spindle headstock and said movingtable, wherein said tool post includes: a supporting member having apair of left and right leg parts positioned on the left and right whenseen in the axis direction and a beam part integrally coupling at leastupper ends of the both leg parts with each other; and a turret to whoseouter circumferential portion a plurality of tools are attached andwhich is supported by the supporting member, and wherein the supportingmember is supported on said bed to be movable in the axis direction, andthe turret is supported to be movable in an up/down (X-axis) directionby turret guide rails disposed on front faces or side faces of the leftand right leg parts.
 2. The machine tool according to claim 1, wherein acutting point of said tool post is positioned vertically under saidfirst spindle headstock.
 3. The machine tool according to claim 1,wherein the supporting member is mounted on a guide rail by which saidmoving table is supported to be movable in the axis direction, lowerportions of the left and right leg parts widen outward in a radialdirection of the turret and protrude toward said moving table sideacross the turret guide rails, and the turret guide rails are disposedon the front faces of the left and right leg parts.
 4. The machine toolaccording to claim 1, wherein a turret ball screw moving the turret inthe up/down direction and a feed motor rotary driving the turret ballscrew are disposed to be deviated toward one side in a left/rightdirection in a space surrounded by the left and right leg parts and thebeam part of the supporting member.
 5. The machine tool according toclaim 4, wherein the turret includes: a turret head to which the toolsare attached; and a rotary indexing mechanism by which the turret headis supported to be rotary indexable, and wherein a rotary indexing motorof the rotary indexing mechanism is disposed on a back face of theturret and is positioned in the space surrounded by the left and rightleg parts and the beam part of the supporting member.
 6. The machinetool according to claim 2, wherein a turret ball screw moving the turretin the up/down direction and a feed motor rotary driving the turret ballscrew are disposed to be deviated toward one side in a left/rightdirection in a space surrounded by the left and right leg parts and thebeam part of the supporting member.
 7. The machine tool according toclaim 6, wherein the turret includes: a turret head to which the toolsare attached; and a rotary indexing mechanism by which the turret headis supported to be rotary indexable, and wherein a rotary indexing motorof the rotary indexing mechanism is disposed on a back face of theturret and is positioned in the space surrounded by the left and rightleg parts and the beam part of the supporting member.
 8. The machinetool according to claim 3, wherein a turret ball screw moving the turretin the up/down direction and a feed motor rotary driving the turret ballscrew are disposed to be deviated toward one side in a left/rightdirection in a space surrounded by the left and right leg parts and thebeam part of the supporting member.
 9. The machine tool according toclaim 8, wherein the turret includes: a turret head to which the toolsare attached; and a rotary indexing mechanism by which the turret headis supported to be rotary indexable, and wherein a rotary indexing motorof the rotary indexing mechanism is disposed on a back face of theturret and is positioned in the space surrounded by the left and rightleg parts and the beam part of the supporting member.